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s� hl 07 December 2001 AGE Project No 96-0232 Page 3 of 9 an underground pipeline from the Rocky's Restaurant property to the Flag City Chevron treatment system Utilizing an estimated ground water extraction radius of influence of 25 feet (Final Remediation Plan, dated 31 August 2001), ground water extraction wells will be placed at the Rocky's Restaurant property as shown in Figure 3 to recover the dissolved MTBE plume in the First Water zone Extracted ground water will be routed underground to the existing Flag City Chevron ground water pump-and-treat system(Figure 2) Treated water will be discharged into the Coldani irrigation ditch, located approximately 500 feet south of the site Water will be discharged under RWQCB General Order 5-00-119 (Figure 5) AGE proposes to extract ground water from both the newly installed off- site extraction wells and the existing Flag City Chevron on-site extraction wells at a total flow rate between 20 and 25 GPM, however it will be necessary to implement a ground water extraction surging method to manage the total water volume treated on-site and off-site and discharged into the Coldam ditch 41 OFF-SITE CLEAN-UP GOALS • The RWQCB stated by letter dated 05 October 2000 (Appendix A) that the California Department of Health Services (DHS) Secondary Maximum Contaminant Level (MCL) for MTBE of 5,ug/1 should be utilized as the clean-up goal for the Flag City Chevron clean-up effort Based on the reported Flag City Chevron pump-and-treat influent-end MTBE concentrations decreasing to concentrations as low as 7 ,ug/l between November 2000 and September 2001, AGE believes that the DHS Secondary Maximum Contaminant Level (MCL) for MTBE of 5 ,ig/l should also be utilized as the "off-site" clean-up goal 4 2 OFF-SITE SECOND ZONE GROUND WATER EXTRACTION AND TREATMENT Initially, AGE does not recommend ground water extraction from the Second Water Zone until ground water remediation of the First Water Zone has been implemented and has been in operation for a sufficient period of time to assess the effect on the impacted Second Water Zone(possibly two to four quarters) AGE has noted a beneficial effect on Second Water Zone onsite with remediation only being conducted on the First Water Zone This implies a potential for vertical migration of impacted water between the two informal hydrological units, therefore AGE believes that ground water extraction from the Second Water Zone may induce additional vertical migration of MTBE- impacted ground water from the First Water Zone to the Second Water Zone Concentrations of dissolved MTBE in the Second Water Zone(40 to 60 feet bsg) and Rocky's Upper Zone (65 to 75 feet bsg) have steadily decreased in samples collected from Rocky's Restaurant • domestic water well (RDW-1), monitoring wells MW-11A, MW-11B and from extraction well Advanced GeoEnvironmental,Inc